Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session A8: Electronic Structure Theory |
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Sponsoring Units: DCOMP Chair: Michael Widom, Carnegie Mellon University Room: 267 |
Monday, March 13, 2017 8:00AM - 8:12AM |
A8.00001: First-principles Studies of the Role of Defects and Impurities on the Optical Properties of Barium Halide Storage Phosphors and Scintillator Materials Andrew Canning, Bharat Medasani, Mauro Del Ben, Edith Bourret, Gregory Bizarri The Eu doped Ba mixed halide family BaBrX (X=F,Cl,Br,I) changes from being a widely used X-ray storage phosphor (BaBrF:Eu) to one of the brightest know new gamma ray detector scintillators (BaBrI:Eu). To help understand these contrasting optical properties and guide in the design of new and improved scintillator detectors, in collaboration with experimental groups, we have performed first principles theoretical studies of these materials. In particular we have studied their electron and hole trapping mechanisms associated with dopants, defects and impurities and how they can explain their very different optical properties. [Preview Abstract] |
Monday, March 13, 2017 8:12AM - 8:24AM |
A8.00002: Ab Initio study on structural, electronic, magnetic and dielectric properties of LSNO within Density Functional Perturbation Theory John Petersen, Friedhelm Bechstedt, J\"urgen Furthm\"uller, Luisa Scolfaro LSNO (La$_{\mathrm{2-x}}$Sr$_{\mathrm{x}}$NiO$_{\mathrm{4}})$ is of great interest due to its colossal dielectric constant (CDC) and rich underlying physics. While being an antiferromagnetic insulator, localized holes are present in the form of stripes in the Ni-O planes which are commensurate with the inverse of the Sr concentration. The stripes are a manifestation of charge density waves with period approximately 1/x and spin density waves with period approximately 2/x. Here, the spin ground state is calculated via LSDA $+$ U with the PAW method implemented in VASP. Crystal structure and the effective Hubbard U parameter are optimized before calculating $\varepsilon_{\mathrm{\infty }}$ within the independent particle approximation. $\varepsilon_{\mathrm{\infty }}$ and the full static dielectric constant (including the lattice polarizability) $\varepsilon _{\mathrm{0}}$ are calculated within Density Functional Perturbation Theory. [Preview Abstract] |
Monday, March 13, 2017 8:24AM - 8:36AM |
A8.00003: Semilocal Density Functional with High Accuracy for Molecules and Solids Jianmin Tao, Guocai Tian, Yuxiang Mo Kohn-Sham density functional theory is the most popular electronic structure theory, due to the excellent balance between computational cost and improvable accuracy. Recently, we have proposed a nonempirical semilocal density functional [1] based on the exchange-correlation hole. The exchange part was essentially derived from the density matrix expansion, while the correlation part is obtained from a modification of the TPSS correlation in the low-density limit. In this talk, I will present our extensive assessment of the performance of this functional on molecules and solids. [1] J. Tao and Y. Mo, PRL 117, 073001 (2016). [Preview Abstract] |
Monday, March 13, 2017 8:36AM - 8:48AM |
A8.00004: Improving the accuracy of ground-state correlation energies within a plane-wave basis set: The electron-hole exchange kernel Dario Rocca, Anant Dixit, Janos Angyan A new formalism was recently proposed to improve random phase approximation (RPA) correlation energies by including approximate exchange effects [1]. Within this framework, by keeping only the electron-hole contributions to the exchange kernel,two approximations can be obtained: An adiabatic connection analog of the second order screened exchange (AC-SOSEX) and an approximate electron-hole time-dependent Hartree-Fock (eh-TDHF). Here we show how this formalism is suitable for an efficient implementation within the plane-wave basis set. The response functions involved in the AC-SOSEX and eh-TDHF equations can indeed be compactly represented by an auxiliary basis set and the explicit calculation of unoccupied states can be avoided by using density functional perturbation theory techniques [2-3]. As shown by several applications to reaction energies and weakly bound dimers, the inclusion of the electron-hole kernel significantly improves the accuracy of ground-state correlation energies with respect to RPA and semi-local functionals.\\[4pt][1] B. Mussard, D. Rocca, G. Jansen, and J. Angyan, J. Chem. Theory Comput. 12, 2191 (2016) \\[0pt][2] Y. Ping, D. Rocca, and G. Galli, Chem. Soc. Rev. 42, 2437 (2013) \\[0pt][3] A. Dixit, J. Angyan, and D. Rocca, J. Chem. Phys. 145, 104105 (2016) [Preview Abstract] |
Monday, March 13, 2017 8:48AM - 9:00AM |
A8.00005: Semi-Local DFT Functionals with Exact-Exchange-Like Features: Beyond the AK13 Rickard Armiento The Armiento-K\"ummel functional from 2013 (AK13) [1] is a non-empirical semi-local exchange functional on generalized gradient approximation form (GGA) in Kohn-Sham (KS) density functional theory (DFT). Recent works have established that AK13 gives improved electronic-structure exchange features over other semi-local methods, with a qualitatively improved orbital description and band structure. For example, the Kohn-Sham band gap is greatly extended, as it is for exact exchange. This talk outlines recent efforts towards new exchange-correlation functionals based on, and extending, the AK13 design ideas. The aim is to improve the quantitative accuracy, the description of energetics, and to address other issues found with the original formulation. [1] R. Armiento and S. K\"ummel, Phys. Rev. Lett. 111, 036402 (2013). [Preview Abstract] |
Monday, March 13, 2017 9:00AM - 9:12AM |
A8.00006: Hybrid functional pseudopotentials Jing Yang, Liang Z. Tan, Andrew M. Rappe The consistency of exchange-correlation functionals used in pseudopotential construction and the actual density functional theory calculation can affect the accuracy of geometric parameters and band gaps of chemical species. However, routine hybrid functional calculations at present use GGA pseudopotentials instead of pseudopotentials constructed from hybrid functional all-electron calculations, because of the lack of a publicly available hybrid functional pseudopotential generator. The mismatch of exchange-correlation functionals between pseudopotential and DFT calculations could lead to systematic errors. We have developed a hybrid functional pseudopotential generator, and present here the first rigorous investigation of pseudopotential density functional consistency for hybrid functionals. We provide benchmarking results of PBE0 pseudopotentials for the G2 dataset and some simple solids. Our results showed that the accuracy of geometric parameters compared to experiment improves when our new PBE0 pseudopotentials are used for PBE0 calculations. Also, the PBE0 pseudopotential has been implemented in OPIUM (http://opium.sourceforge.net). [Preview Abstract] |
Monday, March 13, 2017 9:12AM - 9:24AM |
A8.00007: Fully self-consistent Fermi-orbital self-interaction correction in density-functional theory Zenghui Yang, Mark Pederson, John Perdew Fermi-orbital self-interaction correction(FOSIC) is a new development under the Perdew-Zunger(PZ) SIC framework. It solved the size-extensitivity problem of the traditional PZSIC implementation with minimal extra cost associated with the localization of orbitals. The originally published FOSIC algorithm was not self-consistent. This leads to not fully minimized total energy, and can lead to wrong ordering of states in strongly correlated systems. We developed an algorithm for the fully self-consistent FOSIC calculation and implemented it in the NRLmol code. Thanks to the new numerical algorithm, the computational cost increase is minimal going from non-self-consistent to fully self-consistent. [Preview Abstract] |
Monday, March 13, 2017 9:24AM - 9:36AM |
A8.00008: GW for transition metal oxide perovskites Zeynep Ergonenc, Bongjae Kim, Peitao Liu, Georg Kresse, Cesare Franchini The \emph{ab initio} calculation of quasiparticle (QP) energies is a technically and computationally challenging problem. In condensed matter physics the most widely used approach to determine QP energies is the $GW$ approximation. Although the $GW$ method has been widely applied to many typical semiconductors and insulators, its applications to more complex compounds such as $4d$ and $5d$ (and to a lesser extent 3$d$) perovskites, have been comparatively rare, and its proper use is not well established from a technical point of view. In this work, we have applied the $GW$ method to a representative set of transition-metal perovskites including 3$d$, 4$d$ and 5$d$ compounds with different electron occupancies, magnetic ordering and structural characteristics. We will discuss the proper procedure to obtain converged QP energies and accurate bandgaps, and highlight the difference between norm-conserving and ultrasoft potentials in GW calculations. [Preview Abstract] |
Monday, March 13, 2017 9:36AM - 9:48AM |
A8.00009: First-principles simulations of doping-dependent mesoscale screening of adatoms in graphene Arash Mostofi, Fabiano Corsetti, Dillon Wong, Michael Crommie, Johannes Lischner Adsorbed atoms and molecules play an important role in controlling and tuning the functional properties of 2D materials. Understanding and predicting this phenomenon from theory is challenging because of the need to capture both the local chemistry of the adsorbate-substrate interaction and its complex interplay with the long-range screening response of the substrate. To address this challenge, we have developed a first-principles multi-scale approach that combines linear-scaling density-functional theory, continuum screening theory and large-scale tight-binding simulations. Focussing on the case of a calcium adatom on graphene, we draw comparison between the effect of (i) non-linearity, (ii) intraband and interband transitions, and (iii) the exchange-correlation potential, thus providing insight into the relative importance of these different factors on the screening response. We also determine the charge transfer from the adatom to the graphene substrate (the key parameter used in continuum screening models), showing it to be significantly larger than previous estimates. [Preview Abstract] |
Monday, March 13, 2017 9:48AM - 10:00AM |
A8.00010: Investigation into the inadequacy of cRPA in reproducing screening in strongly correlated systems QIANG HAN, Bismayan Chakrabarti, Kristjan Haule The accuracy of the constrained random phase approximation(cRPA) method is examined in multi-orbital Hubbard models containing all possible on-site density-density interactions.Using DMFT, we show that the effective model constructed using cRPA fails to reproduce the spectral properties of the original full model in a wide parameter range. By comparing quantities such as the density of states and quasiparticle residues of the full and the effective models, we show that cRPA systematically overestimates the screening of Hubbard U for DMFT impurity solvers. We instead examine a new method to estimate the true screening in the system using the local polarization, which is highly successful in reproducing spectra and which also shows that the true screening is far less than that predicted by RPA. Furthermore, we examine the fully screened interaction W using RPA and our new method and show that the RPA W is overscreened and also misses the signatures of local screening, which are clearly present in our new method. [Preview Abstract] |
Monday, March 13, 2017 10:00AM - 10:12AM |
A8.00011: Adaptive molecular dynamics for long time-scale simulations Yuki Sakai, James R. Chelikowsky We propose an adaptive molecular dynamics method that combines classical and first-principles Born-Oppenheimer molecular dynamics. In this adaptive method, classical and Born-Oppenheimer dynamics are performed sequentially and alternately. The parameters of classical model potentials are fitted by using a force-matching method every time after the Born-Oppenheimer molecular dynamics. This method reduces the heavy computational load of the Born-Oppenheimer dynamics while the update of model potential parameters enable one to incorporate the change in bond order and coordination number. By using the current method, we can qualitatively reproduce the power spectra of organic molecules obtained with Born-Oppenheimer molecular dynamics. We also discuss the computational speed up and stability of this method. [Preview Abstract] |
Monday, March 13, 2017 10:12AM - 10:24AM |
A8.00012: Systematic method to improve first principle calculations of materials under extreme conditions Justin Smith, Kieron Burke We develop an exact method for calculating the density and free energy of electronic systems at high temperatures that is used in conjunction with existing computational approaches. This method defines an effective thermal potential (ETP) that is used in an accurate hot temperature solver to get the properties at a colder temperature. In practical calculations, the ETP must be approximated using thermal DFT at the cold and hot temperature which is then fed into a quantum Monte Carlo calculation at the hot temperature to yield better results than thermal DFT alone at the colder temperature of interest. In this work we lay out the formalism of the scheme and provide a proof-of-principle calculation using the asymmetric Hubbard dimer. We show that our method improves the calculations of approximate densities and maintains the accuracy of the free energy. [Preview Abstract] |
Monday, March 13, 2017 10:24AM - 10:36AM |
A8.00013: Multielectron Effects in High Harmonic Generation: A Time-Dependent Density Functional Theory Approach Paul Abanador, Francois Mauger, Kenneth Lopata, Mette Gaarde, Kenneth Schafer Multielectron effects are expected to play a prominent role in processes involving the interaction of molecules with strong laser fields, such as high harmonic generation (HHG). We employ a two-active-orbital model using time-dependent density functional theory (TDDFT) framework for HHG from a diatomic molecule in one-dimension. We find that incorporating dynamical multielectron effects within TDDFT for this prototypical molecular model can lead to a higher cutoff of the harmonic plateau compared to what is expected from a single-active-orbital model. This feature in the HHG spectrum is associated to recombination of the ionized electron wave packet to the orbital with higher ionization potential. We aim to compare the TDDFT results with an extension of our semiclassical model [Phys. Rev. A 93, 043815 (2016)] to multiple active orbitals in order to investigate the role of multielectron effects in the HHG process. [Preview Abstract] |
Monday, March 13, 2017 10:36AM - 10:48AM |
A8.00014: Investigating density functional theory with the density matrix renormalization group Thomas E. Baker, Steven R. White, Kieron Burke Density functional theory (DFT) is an exact, low scaling method for the general purpose of solving quantum mechanical systems, especially computations used for quantum chemical systems. The difficulty in solving for many exact features of the theory in three dimensions can be revealed with analog calculations in one dimension [1,2], since the density matrix renormalization group (DMRG) gives numerically exact answers in one dimension with comparative ease. The current focus has involved constructing proofs of principle for efficient quantum algorithms. Recent progress will be discussed, including machine learning the universal density functional [3] and constructing optimized basis sets from a DFT orbital. [1] E.M.~Stoudenmire, L.O.~Wagner, K.~Burke, and S.R.~White {\it Phys.~Rev.~Lett.} {\bf 109}, 056402 (2012) [2] T.E.~Baker, E.M.~Stoudenmire, L.O.~Wagner, K.~Burke, and S.R.~White {\it Phys.~Rev.~B} {\bf 91}, 235141 (2015) [3] L.~Li, T.E.~Baker, S.R.~White, and K.~Burke, arxiv:1609.03705 [Preview Abstract] |
Monday, March 13, 2017 10:48AM - 11:00AM |
A8.00015: Large-scale DFT calculations using multi-site support functions in CONQUEST Ayako Nakata, David Bowler, Tsuyoshi Miyazaki CONQUEST is a linear-scaling (O(N)) DFT code developed jointly by UCL and NIMS. CONQUEST achieves O(N) by using the locality of density matrices with the density matrix minimization method. Local orbitals which are called support functions are used to express the density matrices and Kohn-Sham orbitals. Our recent study shows that the code can employ DFT calculations on million-atom systems. We have introduced multi-site support functions [Phys. Chem. Chem. Phys. 17, 31427 (2015)], which are the linear combinations of pseudo-atomic orbitals from a target atom and its neighbor atoms. Multi-site support functions correspond to local molecular orbitals so that the number of required support functions can be the minimal. The linear-combination coefficients are optimized numerically while the initial coefficients are determined by using the localized filter diagonalization method [Phys. Rev. B 80, 205104 (2009)]. The accuracy and computational efficiency of the present method are demonstrated by investigating the atomic and electronic properties of hydrated DNA systems containing several thousand atoms. The test calculations of metallic nanoparticles show the applicability of the method to metallic systems. [Preview Abstract] |
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